CHEK1 and medulloblastoma: We conclude from these analyses that both the ATM‐Chk2 and ATR‐Chk1 kinase modules are widely ‘spontaneously’ activated among human paediatric medulloblastomas, thereby suggesting that endogenous DNA double‐strand breaks and replication stress and/or replication‐associated DNA lesions occur commonly in these malignancies, even prior to any radiochemotherapy.